1. Field of the Invention
The present invention relates to a one-pack type epoxide composition.
Epoxides having more than one epoxy groups in their molecule, when combined and mixed with various curing agents, may be cured at ambient temperature or elevated temperature. Since the cured epoxides have excellent adhesion to various materials, they have been used in variety of fields of application such as adhesives and coatings, and in injection, dipping, casting and potting. The present invention is to provide, in the fields relating to epoxides, epoxide compositions which can be easily handled and have excellent curing characteristics. More concretely, the present invention is to provide one-pack type heat curing epoxide compositions which have excellent storage stability and can be cured in a short period of time at relatively low temperature.
2. Description of the Prior Art
Most of the conventionally used epoxide compositions are of two-pack type, and they have to be used immediately after mixing an epoxide and a curing agent or a curing accelerator. Although two-pack type epoxide compositions may be cured at room temperature or at low temperature, they have to be precisely weighed and mixed just prior to use. When wrong amounts are weighed relative to the correct amounts of the epoxide and the curing agent, or subsequent mixing is not sufficient even if correct amounts are weighed, there is a problem that the performance of the cured material is insufficient. Also, limited pot life of conventional two-pack type epoxide compositions makes their adaptability to automated machines difficult. Thus, it is desired to produce one-pack type heat curing epoxide compositions to eliminate these drawbacks.
One-pack type heat curing epoxide compositions need a latent-type curing agent which has a property of not reacting with an epoxide at room temperature but starting reaction to cure upon heating. Some latent-type curing agents have been proposed so far, and typically, there may be mentioned dicyandiamide, dibasic acid dihydrazides, boron trifluoride amine complex salts, guanamines, melamine and imidazoles. Although, mixtures of dicyandiamide, melamine or a guanamine with an epoxide are excellent in storage stability, they have a drawback of necessitating a curing condition at high temperature above 150 .degree. C. for a long period of time. Although, it has been widely done to shorten the curing time by the use of a curing accelerator, this accompanies a drawback that storage stability is extremely damaged. Also, dibasic acid dihydrazides and imidazoles have poor storage stability even though they cure the epoxide at relatively low temperature. Boron trifluoride amine complex salts have advantages of excellent storage stability and short curing time. But the cured materials have poor resistance to water and cause corrosion of metals. Thus, each of curing agents has a drawback. Under such circumstances, it has been desired to develop an epoxide composition which has excellent storage stability, can be cured at low temperature in a short period of time, and yet exhibits good performance when cured.
To eliminate the drawback, it has been proposed to use as a curing agent for polyepoxides a reaction product between a dialkylamine and an epoxide in Japanese Unexamined Patent Publications
Sho 56-155222 and Sho 57-100127 and a reaction product between an alcohol or phenol having a tertiary amino group and a polyepoxide in Sho 59-53526. However, these synthesized curing agents actually did not have good storage stability, and the performance of the cured material was not satisfactory.
Japanese Unexamined Patent Publication Hei 1-254731 discloses that a curing agent prepared by heating and reacting N,N-dialkylaminoalkylamine, an amine having two amino groups and urea is effective as a latent type curing agent. The synthesis of this curing agent is based on a reaction wherein ammonia is removed from the amino-containing substance and urea. Thus, a large amount is lost as ammonia during this reaction and this process is economically disadvantageous because the yield of the objective material is low. It is desired to solve this problem and there is need to develop a synthesis method in which there is no volatile component during the reaction
Thus, it is an object of the present invention to provide a latent type curing agent which is economically advantageous and which, when mixed with an epoxide, provides an epoxide composition that can be cured in a short period of time at relatively low temperature, i.e. from 80.degree. to 120.degree. C. while maintaining good storage stability